Reaktionen von Uranpentabromid Die Kristallstrukturen von PPh₄[UBr₆], PPh₄ [UBr₆] · 2CCl₄, (PPh₄)₂[UBr₆] · 4CH₃CN und (PPh₄)₂[UO₂Br₄] · 2CH₂Cl₂

Abstract

PPh4[UBr6] und PPh4[UBr6] · 2CCl4 wurden aus UBr5 · CH3CN und Tetraphenylphosphonium‐bromid in Dichlormethan erhalten, letzteres nach Zusatz von CCl4. Ihre Kristallstrukturen wurden durch Röntgenbeugung aufgeklärt. PPh4[UBr6]: 2101 beobachtete Reflexe, R = 9,0%, Raumgruppe C2/c, Z = 4, a = 2315,5, b = 695,0, c = 1805,2 pm, β = 96,38°. PPh4[UBr6] · 2CCl4: 2973 Reflexe, R = 7,4%, Raumgruppe P21/c, Z = 4, a = 1111,5, b = 2114,2, c = 1718,7 pm, β = 95,42°. Uranpentabromid wird durch Schwefelwasserstoff zu Urantetrabromid reduziert. Lösungen von UBr5 mit 1 bzw. mehr als 3 Moläquivalenten Acetonitril in Dichlormethan spalten beim Eindampfen Brom ab, dabei entsteht UBr4 · CH3CN bzw. UBr4 · 3CH3CN. Diese reagieren in Acetonitril mit PPh4Br unter Bildung von (PPh4)2[UBr6] · 4CH3CN, dessen Kristallstruktur bestimmt wurde (2663 beobachtete Reflexe, R = 5,0%): Raumgruppe P21/c, Z = 2, a = 981,8, b = 2010,1, c = 1549,3 pm, β = 98,79°. Die Reduktion von Uranpentabromid mit Tetramethylammonium‐hydrogensulfid in Dibrommethan führt zu (NEt4)2[U2Br10], das extrem hydrolyse‐ und sauerstoffempfindlich ist. Ebenso empfindlich ist (PPh4)2[U2Br10], das aus UBr4 und PPh4Br in CH2Cl2 erhalten wurde. Von seinem Oxidationsprodukt (PPh4)2[UO2Br4] · 2CH2Cl2 wurde die Kristallstruktur bestimmt (2163 Reflexe, R = 8,3%): Raumgruppe C2/c, Z = 4, a = 2006,3, b = 1320,6, c = 2042,5 pm, β = 98,78°. Die UBr‐Bindungslängen in den oktaedrischen Anionen be tragen im Mittel 266,2 pm beim UBr6−, 276,7 pm beim UBr62− und 282,5 beim UO2Br42−.

Synthesis and crystal structure of triethylammonium hexabromidouranate(IV) dichloromethane monosolvate

“…The Br-U-Br angles in the octahedron-like polyhedron range from 86.519 (13) to 94.879 14and show a quite significant distortion from the ideal angle of 90 . These atomic distances and angles are in good agreement with the compounds reported previously (Bohrer et al, 1988;Caira et al, 1978). The atomic distances of the two symmetry-independent triethylammonium cations are in good agreement with each other, as well as with the literature, for example in bis(triethylammonium) tetrachloridodioxidouranium(VI) (Gatto et al, 2003;Serezhkina et al, 2010;Bois et al, 1976).…”

“…All these compounds have a slightly distorted octahedron-shaped [UCl 6 ] 2coordination polyhedron in common with Cl-U-Cl angles close to 90 and some of them, like [BuMeIm] 2 [UCl 6 ], feature hydrogenbonding networks or weak hydrogen interactions (Nikitenko et al, 2007). Examples of hexabromidouranates(IV) with organic cations are (PPh 4 ) 2 [UBr 6 ]Á4CH 3 CN (Bohrer et al, 1988), [P(C 6 H 5 ) 3 C 2 H 5 ] 2 [UBr 6 ] (Caira et al, 1978) or (Ph 3 Et-P) 2 [UBr 6 ] (Caira et al, 1978). As in the case of the hexachloridouranates(IV), the [UBr 6 ] 2octahedra show a slight distortion and the compounds feature an extended network of hydrogen bonds.…”

“…As in the case of the hexachloridouranates(IV), the [UBr 6 ] 2octahedra show a slight distortion and the compounds feature an extended network of hydrogen bonds. The only two structurally elucidated examples of hexabromidouranate(V) anions, [UBr 6 ] À , that show significantly shorter U-Br distances compared to [UBr 6 ] 2anions are (Ph 4 P)[UBr 6 ] and (Ph 4 P)[UBr 6 ]Á2CCl 4 (Bohrer et al, 1988). These two compounds as well as (PPh 4 )[UBr 6 ]Á-CH 2 Cl 2 serve as examples for the stability of uranium(V) in organic solvents; however, a reduction of U V to U IV was observed upon removal of the solvent (Bohrer et al, 1988).…”

“…The only two structurally elucidated examples of hexabromidouranate(V) anions, [UBr 6 ] À , that show significantly shorter U-Br distances compared to [UBr 6 ] 2anions are (Ph 4 P)[UBr 6 ] and (Ph 4 P)[UBr 6 ]Á2CCl 4 (Bohrer et al, 1988). These two compounds as well as (PPh 4 )[UBr 6 ]Á-CH 2 Cl 2 serve as examples for the stability of uranium(V) in organic solvents; however, a reduction of U V to U IV was observed upon removal of the solvent (Bohrer et al, 1988). During this reaction, elemental bromine was formed via oxidation besides the adduct UBr 4 ÁCH 3 CN (Bohrer et al, 1988).…”

“…These two compounds as well as (PPh 4 )[UBr 6 ]Á-CH 2 Cl 2 serve as examples for the stability of uranium(V) in organic solvents; however, a reduction of U V to U IV was observed upon removal of the solvent (Bohrer et al, 1988). During this reaction, elemental bromine was formed via oxidation besides the adduct UBr 4 ÁCH 3 CN (Bohrer et al, 1988).…”